Field
Embodiments of the present invention generally relate to apparatuses for supporting a patterning device of a lithographic apparatus and, more particularly, to apparatuses and methods for controlling the temperature of a patterning device by flowing gas across a surface of the patterning device.
Related Art
A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. A lithographic apparatus can be used, for example, to manufacture integrated circuits (ICs). In such a case, a patterning device, for example, a mask or a reticle, can generate a circuit pattern to be formed on an individual layer of the IC. This pattern can be transferred onto a target portion (for example, including part of, one, or several dies) on a substrate (for example, a silicon wafer). Transfer of the pattern is typically via imaging onto a layer of radiation-sensitive material (resist) provided on the substrate. Generally, a single substrate will contain a network of adjacent target portions that are successively patterned. Conventional lithographic apparatuses include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion at once, and so-called scanners, in which each target portion is irradiated by scanning the pattern through a radiation beam in a given direction (the “scanning”-direction) while synchronously scanning the substrate parallel or anti-parallel to this direction. It is also possible to transfer the pattern from the patterning device to the substrate by imprinting the pattern onto the substrate.
The patterning device can comprise a base material, for example, fused silica, that is substantially transparent to radiation, for example, deep ultraviolet radiation, and comprise a pattern made of a substantially non-transparent material, for example, chrome. Typically, the pattern absorbs the radiation, which generates heat. This heat causes the patterning device to expand and can adversely affect the air between the patterning device and proximal lens elements. For example, patterning device expansion can cause image distortion (such as overlay errors). Reticle or wafer alignment, magnification correction, feed forward systems for expansion prediction, and lens correction can partially address such image distortion. But these correction methods do not reduce imaging errors due to heating of the air between the patterning device and the lens element, so as tighter tolerances are required, these correction methods may not adequately address image distortion caused by the patterning device thermal expansion.